View MAX66420910_4547339.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

19-2920; Rev 3; 10/09
KIT ATION EVALU BLE AVAILA
1C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm
General Description
The MAX6642 precise, two-channel digital temperature sensor accurately measures the temperature of its own die and a remote PN junction and reports the temperature data over a 2-wire serial interface. The remote PN junction is typically a substrate PNP transistor on the die of a CPU, ASIC, GPU, or FPGA. The remote PN junction can also be a discrete diode-connected smallsignal transistor. The 2-wire serial interface accepts standard system management bus (SMBusTM), Write Byte, Read Byte, Send Byte, and Receive Byte commands to read the temperature data and to program the alarm thresholds. To enhance system reliability, the MAX6642 includes an SMBus timeout. The temperature data format is 10 bit with the least significant bit (LSB) corresponding to +0.25C. The ALERT output asserts when the local or remote overtemperature thresholds are violated. A fault queue may be used to prevent the ALERT output from setting until two consecutive faults have been detected. Measurements can be done autonomously or in a single-shot mode. Remote accuracy is 1C maximum error between +60C and +100C. The MAX6642 operates from -40C to +125C, and measures remote temperatures between 0C and +150C. The MAX6642 is available in a 6-pin TDFN package with an exposed pad.
Features
o Dual Channel: Measures Remote and Local Temperature o +0.25C Resolution o High Accuracy 1C (max) (Remote) and 2C (Local) from +60C to +100C o Measures Remote Temperature Up to +150C o Programmable Overtemperature Alarm Temperature Thresholds o SMBus/I2C-Compatible Interface o Tiny TDFN Package with Exposed Pad
MAX6642
Ordering Information
PART MAX6642ATT90-T MAX6642ATT92-T MAX6642ATT94-T MAX6642ATT96-T MAX6642ATT98-T MAX6642ATT9A-T MAX6642ATT9C-T MAX6642ATT9E-T TEMP RANGE -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C PIN-PACKAGE 6 TDFN-EP* 6 TDFN-EP* 6 TDFN-EP* 6 TDFN-EP* 6 TDFN-EP* 6 TDFN-EP* 6 TDFN-EP* 6 TDFN-EP*
Applications
Desktop Computers Notebook Computers Servers Thin Clients Test and Measurement Workstations Graphic Cards
T = Tape and reel. *EP = Exposed pad. Pin Configuration and Functional Diagram appear at end of data sheet.
Typical Operating Circuit
3.3V 0.1F 47
Selector Guide
PART MAX6642ATT90-T MAX6642ATT92-T MAX6642ATT94-T MAX6642ATT96-T MAX6642ATT98-T MAX6642ATT9A-T MAX6642ATT9C-T MEASURED TEMP RANGE 0C to +150C 0C to +150C 0C to +150C 0C to +150C 0C to +150C 0C to +150C 0C to +150C TOP MARK AFC AFD AFE AFF AEW AFG AFH AFI
P 2200pF
VCC
10k EACH
DXP
MAX6642
SDA
DATA CLOCK INTERRUPT TO P
SCLK ALERT GND
MAX6642ATT9E-T 0C to +150C SMBus is a trademark of Intel Corp.
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
1C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm MAX6642
ABSOLUTE MAXIMUM RATINGS
All Voltages Referenced to GND VCC ...........................................................................-0.3V to +6V DXP.............................................................-0.3V to (VCC + 0.3V) SCLK, SDA, ALERT ..................................................-0.3V to +6V SDA, ALERT Current ...........................................-1mA to +50mA Continuous Power Dissipation (TA = +70C) 6-Pin TDFN (derate 24.4mW/C above +70C) .........1951mW ESD Protection (all pins, Human Body Model) ................2000V Junction Temperature ......................................................+150C Operating Temperature Range .........................-40C to +125C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC = +3.0V to +5.5V, TA = -40C to +125C, unless otherwise specified. Typical values are at VCC = +3.3V and TA = +25C.) (Note 1)
PARAMETER Supply Voltage Temperature Resolution TRJ = +60C to +100C, TA = +25C to +85C TRJ = 0C to +125C TRJ = +125C to +150C Local Temperature Error Supply Sensitivity of Temperature Error Undervoltage Lockout Threshold Undervoltage Lockout Hysteresis Power-On-Reset (POR) Threshold POR Threshold Hysteresis Standby Supply Current Operating Current Average Operating Current Conversion Time Conversion Rate Remote-Diode Source Current ALERT Output-Low Sink Current Output-High Leakage Current VOL = 0.4V VOL = 0.6V VOH = VCC 1 4 1 mA A tCONV fCONV IRJ High level Low level 80 8 From stop bit to conversion completion 106 SMBus static During conversion VCC falling edge 1.5 UVLO Falling edge of VCC disables ADC 2.4 VCC = 3.3V TA = +60C to +100C TA = 0C to +125C -1.0 -3.0 -3.5 -2.0 -3.0 0.2 2.7 90 2.0 90 3 0.5 260 125 8 100 10 120 12 143 10 1.0 2.4 2.95 SYMBOL VCC CONDITIONS MIN 3.0 0.25 10 +1.0 +3.0 +3.5 +2.0 +3.0 C C/V V mV V mV A mA A ms Hz A C TYP MAX 5.5 UNITS V C Bits
Remote Temperature Error
VCC = 3.3V
2
_______________________________________________________________________________________
1C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +5.5V, TA = -40C to +125C, unless otherwise specified. Typical values are at VCC = +3.3V and TA = +25C.) (Note 1)
PARAMETER Logic Input Low Voltage Logic Input High Voltage Input Leakage Current Output Low Sink Current Input Capacitance SMBus TIMING (Note 2) Serial Clock Frequency Bus Free Time Between STOP and START Condition START Condition Setup Time Repeat START Condition Setup Time START Condition Hold Time STOP Condition Setup Time Clock Low Period Clock High Period Data Setup Time Receive SCLK/SDA Rise Time Receive SCLK/SDA Fall Time Pulse Width of Spike Suppressed SMBus Timeout tSU:STA tHD:STA tSU:STO tLOW tHIGH tHD:DAT tR tF tSP tTIMEOUT SDA low period for interface reset 0 20 28 90% to 90% 10% of SDA to 90% of SCLK 90% of SCLK to 90% of SDA 10% to 10% 90% to 90% (Note 4) fSCLK tBUF (Note 3) 4.7 4.7 50 4 4 4.7 4 250 1 300 50 40 100 kHz s s ns s s s s s s ns ns ms SYMBOL VIL VIH ILEAK IOL CIN VCC = 3.0V VIN = GND or 5.5V VOL = 0.6V 2.2 -1 6 5 +1 CONDITIONS MIN TYP MAX 0.8 UNITS V V A mA pF
MAX6642
SMBus-COMPATIBLE INTERFACE (SCLK and SDA)
Note 1: Note 2: Note 3: Note 4:
All parameters tested at TA = +25C. Specifications over temperature are guaranteed by design. Timing specifications guaranteed by design. The serial interface resets when SCLK is low for more than tTIMEOUT. A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SCLK's falling edge.
_______________________________________________________________________________________
3
1C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm MAX6642
Typical Operating Characteristics
(VCC = 3.3V, TA = +25C, unless otherwise noted.)
STANDBY SUPPLY CURRENT vs. CLOCK FREQUENCY
4.5 SUPPLY CURRENT (A) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.01 0.1 1 10 100 CLOCK FREQUENCY (kHz)
MAX6642 toc01
REMOTE TEMPERATURE ERROR vs. REMOTE-DIODE TEMPERATURE
MAX6642 toc02
5.0
2 1 TEMPERATURE ERROR (C) 0 -1 -2 -3 2N3906 -4 0 25 50 75 100 125 TEMPERATURE (C)
LOCAL TEMPERATURE ERROR vs. DIE TEMPERATURE
MAX 6642 toc03
TEMPERATURE ERROR vs. POWER-SUPPLY NOISE FREQUENCY
MAX6642 toc04
3 2 TEMPERATURE ERROR (C) 1 0 -1 -2 -3 0 25 50 75 100
2.0 1.5 TEMPERATURE ERROR (C) 1.0 0.5 0 -0.5 -1.0 VIN = 100mVP-P SQUARE WAVE APPLIED TO VCC WITH NO BYPASS CAPACITOR 0.01 0.1 1 10 LOCAL ERROR REMOTE ERROR
125
-1.5 0.0001 0.001
100
TEMPERATURE (C)
FREQUENCY (kHz)
TEMPERATURE ERROR vs. DXP NOISE FREQUENCY
MAX6642 toc05
TEMPERATURE ERROR vs. DXP-GND CAPACITANCE
1.0 TEMPERATURE ERROR (C) 0 -1.0 -2.0 -3.0 -4.0 -5.0 -6.0
MAX6642 toc06
100 90 TEMPERATURE ERROR (C) 80 70 60 50 40 30 20 10 0 0.001 0.01 0.1 1 10 LOCAL ERROR REMOTE ERROR VIN = AC-COUPLED TO DXP VIN = 100mVP-P SQUARE WAVE
2.0
100
0.1
1
10
100
FREQUENCY (kHz)
DXP-GND CAPACITANCE (nF)
4
_______________________________________________________________________________________
1C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm
Pin Description
PIN 1 2 3 4 5 6 -- NAME VCC GND DXP SCLK SDA ALERT EP FUNCTION Supply Voltage Input, +3V to +5.5V. Bypass VCC to GND with a 0.1F capacitor. A 47 series resistor is recommended but not required for additional noise filtering. Ground Combined Remote-Diode Current Source and ADC Input for Remote-Diode Channel. Place a 2200pF capacitor between DXP and GND for noise filtering. SMBus Serial-Clock Input. May be pulled up to +5.5V regardless of VCC. SMBus Serial-Data Input/Output, Open Drain. May be pulled up to +5.5V regardless of VCC. SMBus Alert (Interrupt) Output, Open Drain. ALERT asserts when temperature exceeds user-set limits. See the ALERT Interrupts section. Exposed Pad. Internally connected to GND. Connect to a PCB ground pad for optimal performance. Not intended as an electrical connection point.
MAX6642
Detailed Description
The MAX6642 is a temperature sensor for local and remote temperature-monitoring applications. Communication with the MAX6642 occurs through the SMBus-compatible serial interface and dedicated alert pins. ALERT asserts if the measured local or remote temperature is greater than the software-programmed ALERT limit. The MAX6642 converts temperatures to digital data either at a programmed rate of eight conversions per second or in single conversions. Temperature data is represented by 8 data bits (at addresses 00h and 01h), with the LSB equal to +1C and the MSB equal to +128C. Two additional bits of remote temperature data are available in the "extended" register at address 10h and 11h (Table 2) providing resolution of +0.25C.
remote temperature is measured eight times per second. The results of the previous conversion are always available, even if the ADC is busy.
Low-Power Standby Mode
Standby mode reduces the supply current to less than 10A by disabling the ADC and timing circuitry. Enter standby mode by setting the RUN bit to 1 in the configuration byte register (Table 4). All data is retained in memory, and the SMBus interface is active and listening for SMBus commands. Standby mode is not a shutdown mode. With activity on the SMBus, the device draws more supply current (see the Typical Operating Characteristics). In standby mode, the MAX6642 can be forced to perform ADC conversions through the one-shot command, regardless of the RUN bit status. If a standby command is received while a conversion is in progress, the conversion cycle is truncated, and the data from that conversion is not latched into a temperature register. The previous data is not changed and remains available. Supply-current drain during the 125ms conversion period is 500A (typ). In standby mode, supply current drops to 3A (typ).
ADC and Multiplexer
The averaging ADC integrates over a 60ms period (each channel, typ), with excellent noise rejection. The multiplexer automatically steers bias currents through the remote and local diodes. The ADC and associated circuitry measure each diode's forward voltage and compute the temperature based on this voltage. Both channels are automatically converted once the conversion process has started, either in free-running or single-shot mode. If one of the two channels is not used, the device still performs both measurements, and the user can ignore the results of the unused channel. If the remote-diode channel is unused, connect DXP to GND rather than leaving DXP open. The conversion time per channel (remote and internal) is 125ms. If both channels are being used, then each channel is converted four times per second. If the external conversion-only option is selected, then the
SMBus Digital Interface
From a software perspective, the MAX6642 appears as a set of byte-wide registers that contain temperature data, alarm threshold values, and control bits. A standard SMBus-compatible 2-wire serial interface is used to read temperature data and write control bits and alarm threshold data. The MAX6642 employs four standard SMBus protocols: Write Byte, Read Byte, Send Byte, and Receive Byte. (Figures 1, 2, and 3). The shorter Receive Byte protocol allows quicker transfers, provided that the correct data
5
_______________________________________________________________________________________
1C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm MAX6642
WRITE BYTE FORMAT
S ADDRESS 7 BITS SLAVE ADDRESS: EQUIVALENT TO CHIP-SELECT LINE OF A 3-WIRE INTERFACE WR ACK COMMAND 8 BITS ACK DATA 8 BITS DATA BYTE: DATA GOES INTO THE REGISTER SET BY THE COMMAND BYTE (TO SET THRESHOLDS, CONFIGURATION MASKS, AND SAMPLING RATE) COMMAND 8 BITS COMMAND BYTE: SELECTS WHICH REGISTER YOU ARE REDING FROM ACK S ADDRESS 7 BITS SLAVE ADDRESS: REPEATED DUE TO CHANGE IN DATAFLOW DIRECTION RD ACK DATA 8 BITS DATA BYTE: READS FROM THE REGISTER SET BY THE COMMAND BYTE /// P ACK P 1
READ BYTE FORMAT
S ADDRESS 7 BITS SLAVE ADDRESS: EQUIVALENT TO CHIP SELECT LINE WR ACK
SEND BYTE FORMAT
S ADDRESS 7 BITS WR ACK COMMAND 8 BITS COMMAND BYTE: SENDS COMMAND WITH NO DATA, USUALLY USED FOR ONE-SHOT COMMAND S = START CONDITION P = STOP CONDITION SHADED = SLAVE TRANSMISSION /// = NOT ACKNOWLEDGED ACK P
RECEIVE BYTE FORMAT
S ADDRESS 7 BITS RD ACK DATA 8 BITS DATA BYTE: READS DATA FROM THE REGISTER COMMANDED BY THE LAST READ BYTE OR WRITE BYTE TRANSMISSION; ALSO USED FOR SMBUS ALERT RESPONSE RETURN ADDRESS /// P
Figure 1. SMBus Protocols
A tLOW
B tHIGH
C
D
E
F
G
H
I
J
K
L
M
SMBCLK
SMBDATA
tSU:STA tHD:STA A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE
tSU:DAT E = SLAVE PULLS SMBDATA LINE LOW F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO SLAVE H = LSB OF DATA CLOCKED INTO SLAVE I = SLAVE PULLS DATA LINE LOW J = ACKNOWLEDGE CLOCKED INTO MASTER K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION M = NEW START CONDITION
tSU:STO
tBUF
Figure 2. SMBus Write Timing Diagram
6 _______________________________________________________________________________________
1C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm
register was previously selected by a Write Byte instruction. Use caution when using the shorter protocols in multimaster systems, as a second master could overwrite the command byte without informing the first master. Read temperature data from the read internal temperature (00h) and read external temperature (01h) registers. The temperature data format for these registers is 8 bits for each channel, with the LSB representing +1C (Table 1). Read the additional bits from the read extended temperature byte register (10h, 11h), which extends the data to 10 bits and the resolution to +0.25C per LSB (Table 2). When a conversion is complete, the main temperature register and the extended temperature register are updated.
Table 1. Main Temperature Register (High Byte) Data Format
TEMP (C) 130.00 127.00 126.00 25 0.00 <0.00 Diode fault (short or open) DIGITAL OUTPUT 1 000 0010 0 111 1111 0 111 1110 0 001 1001 0 000 0000 0 000 0000 1 111 1111
MAX6642
Table 2. Extended Resolution Temperature Register (Low Byte) Data Format
FRACTIONAL TEMP (C) 0.000 0.250 0.500 0.750 DIGITAL OUTPUT 00XX XXXX 01XX XXXX 10XX XXXX 11XX XXXX
Alarm Threshold Registers
Two registers store ALERT threshold values--one each for the local and remote channels. If either measured temperature equals or exceeds the corresponding ALERT threshold value, the ALERT interrupt asserts unless the ALERT bit is masked. The power-on-reset (POR) state of the local ALERT THIGH register is +70C (0100 0110). The POR state of the remote ALERT THIGH register is +120C (0111 1000).
present upon power-up, the fault is not indicated until the end of the first conversion. Diode faults do not set the ALERT output.
Diode Fault Detection
A continuity fault detector at DXP detects an open circuit on DXP, or a DXP short to VCC or GND. If an open or short circuit exists, the external temperature register is loaded with 1111 1111 and status bit 2 (OPEN) of the status byte is set to 1. Immediately after POR, the status register indicates that no fault is present. If a fault is
A B C D E F
ALERT Interrupts
The ALERT interrupt occurs when the internal or external temperature reading exceeds a high temperature limit (user programmed). The ALERT interrupt output signal is latched and can be cleared only by reading the status register after the fault condition no longer exists or by successfully responding to the alert response address. If
G H I J K
tLOW
tHIGH
SMBCLK
SMBDATA tSU:STA tHD:STA tSU:DAT tHD:DAT F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO MASTER H = LSB OF DATA CLOCKED INTO MASTER
tSU:STO tBUF I = ACKNOWLEDGE CLOCK PULSE J = STOP CONDITION K = NEW START CONDITION
A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE E = SLAVE PULLS SMBDATA LINE LOW
Figure 3. SMBus Read Timing Diagram
_______________________________________________________________________________________ 7
1C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm MAX6642
Table 3. Command-Byte Assignments
ADDRESS 00h 01h 02h 03h 05h 07h 09h 0Bh 0Dh 0Fh 10h 11h FEh POR STATE 00h (0000 0000) 00h (0000 0000) N/A 10h (0001 0000) 46h (0100 0110) +70C 78h (0111 1000) +120C N/A N/A N/A N/A 0000 0000 0000 0000 4Dh (0100 1101) FUNCTION Read local temperature Read remote temperature Read status byte Read configuration byte Read local high limit Read remote high limit Write configuration byte Write local high limit Write remote high limit Single shot Read remote extended temperature Read internal extended temperature Read manufacturer ID
the ALERT is cleared by responding to the alert response address and the temperature fault condition still exists, ALERT is reasserted after the next temperature-monitoring cycle. To clear ALERT while the temperature is above the trip threshold, write a new high limit that is higher than the current temperature. The ALERT output is open drain, allowing multiple devices to share a common interrupt line.
Alert Response Address
The SMBus alert response interrupt pointer provides quick fault identification for simple slave devices like temperature sensors. Upon receiving an ALERT interrupt signal, the host master can broadcast a Receive Byte transmission to the alert response slave address (0001 100). Following such a broadcast, any slave device that generated an interrupt attempts to identify itself by putting its own address on the bus. The alert response can activate several different slave devices simultaneously, similar to the I2C General Call. If more than one slave attempts to respond, bus arbitra-
Table 4. Configuration-Byte Bit Assignments
BIT 7 (MSB) 6 5 NAME MASK1 STOP/RUN External only Fault queue -- POR STATE 0 0 0 FUNCTION A 1 masks off (disables) the ALERT interrupts. A 1 puts the MAX6642 into standby mode. A 1 disables local temperature measurements so that only remote temperature is measured. The measurement rate becomes 8Hz. 0: ALERT is set by a single fault. 1: Two consecutive faults are required to set ALERT. Reserved.
4 3 to 0
1 0000
Table 5. Status-Byte Bit Assignments
BIT 7 (MSB) 6 5 4 3 2 1 to 0 NAME BUSY LHIGH -- RHIGH -- OPEN -- POR STATE 0 0 0 0 0 0 0 FUNCTION A 1 indicates the MAX6642 is busy converting. A 1 indicates an internal high-temperature fault. Clear LHIGH with a POR or by reading the status byte. Reserved. A 1 indicates an external high-temperature fault. Clear RHIGH with a POR or by reading the status byte. Reserved. A 1 indicates a diode open condition. Clear OPEN with a POR or by reading the status byte when the condition no longer exists. Reserved.
8
_______________________________________________________________________________________
1C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm
tion rules apply, and the device with the lower address code wins. The losing device does not generate an acknowledge and continues to hold the ALERT line low until cleared. (The conditions for clearing an ALERT vary depending on the type of slave device.) Successful completion of the alert response protocol clears the interrupt latch. If the condition still exists, the device reasserts the ALERT interrupt at the end of the next conversion.
Status Byte Functions
The status byte register (Table 5) indicates which (if any) temperature thresholds have been exceeded. This byte also indicates whether the ADC is converting and whether there is an open-circuit fault detected on the external sense junction. After POR, the normal state of all flag bits is zero, assuming no alarm conditions are present. The status byte is cleared by any successful read of the status byte after the overtemperature fault condition no longer exists.
MAX6642
Command Byte Functions
The 8-bit command byte register (Table 3) is the master index that points to the various other registers within the MAX6642. The register's POR state is 0000 0000, so a Receive Byte transmission (a protocol that lacks the command byte) that occurs immediately after POR returns the current local temperature data.
Slave Addresses
The MAX6642 has eight fixed addresses available. These are shown in Table 6. The MAX6642 also responds to the SMBus alert response slave address (see the Alert Response Address section).
Single-Shot
The single-shot command immediately forces a new conversion cycle to begin. If the single-shot command is received while the MAX6642 is in standby mode (RUN bit = 1), a new conversion begins, after which the device returns to standby mode. If a single-shot conversion is in progress when a single-shot command is received, the command is ignored. If a single-shot command is received in autonomous mode (RUN bit = 0), the command is ignored.
POR and UVLO
To prevent ambiguous power-supply conditions from corrupting the data in memory and causing erratic behavior, a POR voltage detector monitors VCC and clears the memory if VCC falls below 2.1 (typ). When power is first applied and VCC rises above 2.1 (typ), the logic blocks begin operating, although reads and writes at VCC levels below 3V are not recommended. A second VCC comparator, the ADC undervoltage lockout (UVLO) comparator prevents the ADC from converting until there is sufficient headroom (VCC = +2.7V typ).
Configuration Byte Functions
The configuration byte register (Table 4) is a read-write register with several functions. Bit 7 is used to mask (disable) interrupts. Bit 6 puts the MAX6642 into standby mode (STOP) or autonomous (RUN) mode. Bit 5 disables local temperature conversions for faster (8Hz) remote temperature monitoring. Bit 4 prevents setting the ALERT output until two consecutive measurements result in fault conditions.
Power-Up Defaults
Power-up defaults include: * ALERT output is cleared. * ADC begins autoconverting at a 4Hz rate. * Command byte is set to 00h to facilitate quick local Receive Byte queries. * Local (internal) THIGH limit set to +70C. * Remote (external) THIGH limit set to +120C.
Table 6. Slave Address
PART NO. SUFFIX MAX6642ATT90 MAX6642ATT92 MAX6642ATT94 MAX6642ATT96 MAX6642ATT98 MAX6642ATT9A MAX6642ATT9C MAX6642ATT9E ADDRESS 1001 000 1001 001 1001 010 1001 011 1001 100 1001 101 1001 110 1001 111
Applications Information
Remote-Diode Selection
The MAX6642 can directly measure the die temperature of CPUs and other ICs that have on-board temperaturesensing diodes (see the Typical Operating Circuit) or they can measure the temperature of a discrete diodeconnected transistor.
Effect of Ideality Factor The accuracy of the remote temperature measurements depends on the ideality factor (n) of the remote "diode" (actually a transistor). The MAX6642 is optimized for n = 1.008, which is the typical value for the Intel Pentium
9
_______________________________________________________________________________________
1C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm
III. A thermal diode on the substrate of an IC is normally a PNP with its collector grounded. Connect the anode (emitter) to DXP and the cathode to GND of the MAX6642. If a sense transistor with an ideality factor other than 1.008 is used, the output data is different from the data obtained with the optimum ideality factor. Fortunately, the difference is predictable. Assume a remote-diode sensor designed for a nominal ideality factor nNOMINAL is used to measure the temperature of a diode with a different ideality factor n1. The measured temperature TM can be corrected using: n1 TM = TACTUAL nNOMINAL where temperature is measured in Kelvin and nNOMIMAL for the MAX6642 is 1.008. As an example, assume you want to use the MAX6642 with a CPU that has an ideality factor of 1.002. If the diode has no series resistance, the measured data is related to the real temperature as follows: n 1.008 TACTUAL = TM NOMINAL = TM = 1.002 n1 TM (1.00599) For a real temperature of +85C (358.15K), the measured temperature is +82.91C (356.02K), an error of -2.13C. for a diode temperature of +85C. In this example, the effect of the series resistance and the ideality factor partially cancel each other.
MAX6642
Table 7. Remote-Sensor Transistor Manufacturers
MANUFACTURER Central Semiconductor (USA) Rohm Semiconductor (USA) Samsung (Korea) Siemens (Germany) Zetex (England) MODEL NO. CMPT3906 SST3906 KST3906-TF SMBT3906 FMMT3906CT-ND
Note: Discrete transistors must be diode connected (base shorted to collector).
3 x 0.453
C = +1.36C
The effects of the ideality factor and series resistance are additive. If the diode has an ideality factor of 1.002 and series resistance of 3, the total offset can be calculated by adding error due to series resistance with error due to ideality factor: 1.36C - 2.13C = -0.77C
Discrete Remote Diodes
When the remote-sensing diode is a discrete transistor, connect its collector and base together. Table 7 lists examples of discrete transistors that are appropriate for use with the MAX6642. The transistor must be a small-signal type with a relatively high forward voltage; otherwise, the A/D input voltage range can be violated. The forward voltage at the highest expected temperature must be greater than 0.25V at 10A, and at the lowest expected temperature, the forward voltage must be less than 0.95V at 100A. Large power transistors must not be used. Also, ensure that the base resistance is less than 100. Tight specifications for forward current gain (50 < <150, for example) indicate that the manufacturer has good process controls and that the devices have consistent VBE characteristics. Manufacturers of discrete transistors do not normally specify or guarantee ideality factor. This is normally not a problem since good-quality discrete transistors tend to have ideality factors that fall within a relatively narrow
Effect of Series Resistance Series resistance in a sense diode contributes additional errors. For nominal diode currents of 10A and 100A, the change in the measured voltage due to series resistance is:
VM = RS (100A - 10A) = 90A RS Since +1C corresponds to 198.6V, series resistance contributes a temperature offset of: V = 0.453 C V 198.6 C 90 Assume that the diode being measured has a series resistance of 3. The series resistance contributes an offset of:
10
______________________________________________________________________________________
1C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm
range. We have observed variations in remote temperature readings of less than 2C with a variety of discrete transistors. Still, it is good design practice to verify good consistency of temperature readings with several discrete transistors from any manufacturer under consideration. 5) Route through as few vias and crossunders as possible to minimize copper/solder thermocouple effects. 6) When introducing a thermocouple, make sure that both the thermal diode paths have matching thermocouples. A copper-solder thermocouple exhibits 3V/C, and it takes about 200V of voltage error at DXP to cause a +1C measurement error. Adding a few thermocouples causes a negligible error. 7) Use wide traces. Narrow traces are more inductive and tend to pick up radiated noise. The 10-mil widths and spacing recommended in Figure 4 are not absolutely necessary, as they offer only a minor improvement in leakage and noise over narrow traces. Use wider traces when practical. 8) Add a 47 resistor in series with VCC for best noise filtering (see the Typical Operating Circuit). 9) Copper cannot be used as an EMI shield; only ferrous materials such as steel work well. Placing a copper ground plane between the DXP-DXN traces and traces carrying high-frequency noise signals does not help reduce EMI.
MAX6642
ADC Noise Filtering
The integrating ADC used has good noise rejection for low-frequency signals such as 60Hz/120Hz power-supply hum. In noisy environments, high-frequency noise reduction is needed for high-accuracy remote measurements. The noise can be reduced with careful PCB layout and proper external noise filtering. High-frequency EMI is best filtered at DXP with an external 2200pF capacitor. Larger capacitor values can be used for added filtering, but do not exceed 3300pF because excessive capacitance can introduce errors due to the rise time of the switched current source. Nearly all noise sources tested cause the temperature conversion results to be higher than the actual temperature, typically by +1C to +10C, depending on the frequency and amplitude (see the Typical Operating Characteristics).
PCB Layout
Follow these guidelines to reduce the measurement error of the temperature sensors: 1) Connect the thermal-sense diode to the MAX6642 using two traces--one between DXP and the anode, the other between the MAX6642's GND and the cathode. Do not connect the cathode to GND at the sense diode. 2) Place the MAX6642 as close as is practical to the remote thermal diode. In noisy environments, such as a computer motherboard, this distance can be 4in to 8in (typ). This length can be increased if the worst noise sources are avoided. Noise sources include CRTs, clock generators, memory buses, and ISA/PCI buses. 3) Do not route the thermal diode lines next to the deflection coils of a CRT. Also, do not route the traces across fast digital signals, which can easily introduce a 30C error, even with good filtering. 4) Route the thermal diode traces in parallel and in close proximity to each other, away from any higher voltage traces, such as +12VDC. Leakage currents from PCB contamination must be dealt with carefully since a 20M leakage path from DXP to ground causes about +1C error. If high-voltage traces are unavoidable, connect guard traces to GND on either side of the DXP trace (Figure 4).
Twisted-Pair and Shielded Cables
Use a twisted-pair cable to connect the remote sensor for remote-sensor distances longer than 8in or in very noisy environments. Twisted-pair cable lengths can be between 6ft and 12ft before noise introduces excessive errors. For longer distances, the best solution is a shielded twisted pair like that used for audio microphones. For example, Belden #8451 works well for distances up to 100ft in a noisy environment. At the device, connect the twisted pair to DXP and GND and the shield to GND. Leave the shield unconnected at the remote diode. For very long cable runs, the cable's parasitic capacitance often provides noise filtering, so the 2200pF capacitor can often be removed or reduced in value.
GND 10 mils 10 mils THERMAL DIODE ANODE/DXP MINIMUM 10 mils THERMAL DIODE CATHODE/GND 10 mils GND
Figure 4. Recommended DXP PC Traces
11
______________________________________________________________________________________
1C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm MAX6642
Cable resistance also affects remote-sensor accuracy. For every 1 of series resistance, the error is approximately 1/2C. Self-heating does not significantly affect measurement accuracy. Remote-sensor self-heating due to the diode current source is negligible. For the local diode, the worst-case error occurs when autoconverting at the fastest rate and simultaneously sinking maximum current at the ALERT output. For example, with V CC = +5.0V, at an 8Hz conversion rate and with ALERT sinking 1mA, the typical power dissipation is: 5.0V x 450A + 0.4V x 1mA = 2.65mW oJ-A for the 6-pin TDFN package is about +41C/W, so assuming no copper PCB heat sinking, the resulting temperature rise is: T = 2.65mW x 41C/W = +0.11C Even under nearly worst-case conditions, it is difficult to introduce a significant self-heating error.
Thermal Mass and Self-Heating
When sensing local temperature, this device is intended to measure the temperature of the PCB to which it is soldered. The leads provide a good thermal path between the PCB traces and the die. Thermal conductivity between the die and the ambient air is poor by comparison, making air temperature measurements impractical. Because the thermal mass of the PCB is far greater than that of the MAX6642, the device follows temperature changes on the PCB with little or no perceivable delay. When measuring temperature of a CPU or other IC with an on-chip sense junction, thermal mass has virtually no effect; the measured temperature of the junction tracks the actual temperature within a conversion cycle. When measuring temperature with discrete remote sensors, smaller packages, such as SOT23s, yield the best thermal response times. Take care to account for thermal gradients between the heat source and the sensor, and ensure that stray air currents across the sensor package do not interfere with measurement accuracy.
12
______________________________________________________________________________________
1C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm
Functional Diagram
VCC
MAX6642
2 MUX REMOTE ADC LOCAL DIODE FAULT ALERT S Q R REGISTER BANK COMMAND BYTE REMOTE TEMPERATURE 7 8 8 READ WRITE CONTROL LOGIC
DXP
SMBus SDA SCLK
MAX6642
LOCAL TEMPERATURE ALERT THRESHOLD ALERT RESPONSE ADDRESS ADDRESS DECODER
Pin Configuration
PROCESS: BiCMOS
TOP VIEW MAX6642
Chip Information
Package Information
6 5
EP* ALERT
VCC GND
1 2 3
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE PACKAGE CODE T633-2 DOCUMENT NO. 21-0137
SDA
6 TDFN-EP
DXP
4
SCLK
TDFN-EP
*EXPOSED PAD CONNECTED TO GND.
______________________________________________________________________________________
13
1C, SMBus-Compatible Remote/Local Temperature Sensor with Overtemperature Alarm MAX6642
Revision History
REVISION NUMBER 0 1 2 3 REVISION DATE 8/03 10/08 7/09 10/09 Initial release Added missing EP description to Ordering Information and Pin Description, removed the transistor count on page 12, and corrected some minor style issues Corrected errors in Figures 2 and 3 Corrected error in Package Information table DESCRIPTION PAGES CHANGED -- 1, 5, 9, 10, 12 6, 7 13
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

▲Up To Search▲

Price & Availability of MAX66420910

	To Download MAX66420910 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .